In the exploration for and the drilling of hydrocarbon containing substrates at offshore sites, normally test borings are made, or exploratory wells are drilled directly into a subterranean formation. Scientific testing methods will thereafter be used to determine its hydrocarbon content. Depending on the amount of hydrocarbon which is determined to be held in the formation, one or more wells can be drilled for production purposes.
If the formation is determined to be relatively large or productive, it might be economically desirable to build and set a structure or platform which is capable of drilling a desired number of wells at the offshore site whereby to realize maximum production.
Such platforms can be massive, depending on water depth. The overall cost is relatively expensive, dependent on the water depth. After the field or formation has become depleted, however, disposing of a piled structure can be expensive depending on environmental requirements, and once again on the depth of the water in which the structure is set.
In some instances the productivity of a field does not justify furnishing a structure capable of drilling the necessary subsea wells. An economic alternative is to merely drill individual wells which are positioned a set distance from a previously erected structure. Thereafter, produced fluid is moved by pipeline to the platform or structure. It can then be processed, treated and shipped or pipelined to a shore base.
In the instance of satellite subsea wells of this type the wells can be drilled by any one of a variety of drilling vessels. Preferably a vessel of the semisubmersible type can be positioned above the wall site and the drilling operation carried out. In such an arrangement it is necessary to extend a riser column from the well to the water's surface. A rotating drill string can then be lowered into the formation.
It may in some instances be determined economically worthwhile to produce a field and still utilize a remote existing marine structure or even a pipeline to carry produced fluids to shore. Thus, a number of wells can still be drilled into the formation to achieve maximum production.
Any offshore well drilling operation is substantially facilitated through use of a drilling template which is lowered to the ocean floor. The function of a multi-slot template is to provide a series of rigidly positioned, ring-like conductor guides. The latter are spaced one from the other a predetermined distance in a predetermined pattern or arrangement.
Functionally, a drill string is lowered through a conductor, which has been preset with the aid of the template. Thereafter, a rotating drill string can be diverted into a desired direction toward a particular part of the field or formation.
In either instance, as each well is completed through a template slot, the well is provided with the necessary casing, well head, and eventually a Christmas tree.
At this point in an operation, once the well is either producing or has been plugged for future use, an adjacent well can be drilled through another ring-like guide in the template, following the same procedure.
Over a period of time, if a field proves economically productive, the template is utilized until each slot or drilling guide opening accommodates a well. Beyond this point, the template is of no further use except to position Christmas trees, manifolds, and other equipment which might be utilized to gather produced fluids.
Toward alleviating the expense of providing a fixed drilling template which is abandoned after being used, and to facilitate the driling of a group of relatively closely spaced wells into the ocean floor, there is presently provided a provisional template or conductor guide which is sufficiently flexible to be reused and readjusted. The guide can also be used through being repositioned from a fixed well, to provide a pattern of wells over which a jacket can be subsequently lowered.
In brief, the subsea conductor guide apparatus embodies means for poisitioning a conductor or drill pipe which is lowered from a vessel at the surface of the water, to the ocean floor. When so positioned, the upper end of the drill pipe engages a drilling vessel such as a semisubmersible unit. The well can then be drilled by registering a conductor into the drill pipe and lowering a rotating drill string through the guide conductor toward the productive formation.
Upon completion of the first well of a group or pattern, the instant provisional conductor guide apparatus is removably engaged onto the drill pipe or casing of the completed well. This is achieved in a manner that the guide apparatus can be initially rotated about the completed drill pipe. An ancillary guide collar which depends from the unit is then vertically aligned with the next well location.
As each well in the preset pattern is progressively drilled, the provisional conductor guide apparatus is unclamped from its original position and either rotated about the original well or transferred onto the drill pipe of a second well.
It is therefore an object of the invention to provide means for drilling a group of wells to reach an offshore subterranean formation without the use of a permanently submerged template.
A further object is to provide a provisional drilling template of the type contemplated which depends from an initially drilled well whereby to determine the spacing between the two.
A still further object is to provide a well conductor guide which is provisionally connected to a well at the ocean floor whereby to foster the completion of other wells in a desired, relatively closely arranged pattern.